Excessive current within an electric machine may damage electrical components and/or demagnetise any permanent magnets. Accordingly, electric machines typically include an arrangement that prevents current in the electric machine from exceeding a threshold.
One such arrangement involves the use of hardware to chop the current in the electric machine between an upper threshold and a lower threshold. However, hardware increases the component cost of the electric machine. Additionally, in order to chop between upper and lower thresholds, a current sensor is required on each arm of the inverter used to excite the electric machine.
As an alternative to hardware, software may be used to control the current in the electric machine. The software typically employs a predetermined open-loop process that generates a PWM signal to limit the current in the electric machine. A potential problem with this approach is that, in being an open-loop process, the software is insensitive to the current in the winding and cannot therefore detect or respond to an overcurrent event.